Few smokers are unaware of the dangers of cigarettes. Many, however, find themselves powerfully addicted and unable to quit.

So they often try to protect themselves by opting for so-called light or ultra-light cigarettes, believing they provide less harmful tar and nicotine. But in fact, smokers inhale far more nicotine than they realize, research shows. Almost all cigarettes deliver high levels of nicotine, even those labeled light or mild, according to a report last week from the Massachusetts Department of Public Health.

New methods for measuring nicotine, which better simulate how people really smoke, suggest that cigarettes may provide about twice the level of nicotine estimated by traditional testing methods, according to the report. Traditional tests found that smokers took in an average of 0.90 milligrams of nicotine per cigarette, but the Massachusetts method found that cigarettes provide about 1.89 milligrams.

The method takes into account that cigarettes, unlike medicine capsules, don't provide a fixed dose of drug. The amount of nicotine that cigarettes deliver is heavily affected by the way smokers hold and puff them.

In traditional tests, tiny vent holes allow outside air to pass through cigarettes, diluting the amount of nicotine measured, says Matthew Myers, president of the Campaign for Tobacco-Free Kids.

In real life, though, smokers often unconsciously cover these vents with their lips or fingers, delivering a much more concentrated hit of nicotine, says Sally Fogarty, associate commissioner of Massachusetts' public health department. The vents are often too small to see.

Smokers also may increase their intake of nicotine by breathing longer and more deeply, the report shows. Because they inhale smoke deeper into their lungs, their cancers tend to develop lower as well, says Thomas Glynn, American Cancer Society's director of cancer science and trends. Smokers who take shallow puffs tend to develop cancer in the upper part of their lungs.

Because of these practices, the new study shows, there's no significant difference in the amount of nicotine inhaled from light or regular cigarettes.

About 93% of cigarette brands have high nicotine levels — even though 85 of 179 brands tested were labeled light, ultra-light, medium or mild.

"Virtually all cigarettes on the marketplace today deliver moderate to high doses of nicotine sufficient to cause and maintain heavy dependence," the report states.

Myers says the report reinforces U.S. District Judge Gladys Kessler's opinion last month that tobacco companies must stop claiming that cigarettes advertised as "light," "low tar," "mild," and "natural" are less dangerous than other kinds.

The report also finds that the amount of nicotine inhaled by smokers increased by an average of 10% — from 1.72 milligrams in 1998 to 1.89 milligrams in 2004 — and some brands increased as much as 36%.

Jennifer Golisch, a spokeswoman for Philip Morris USA, says the company is reviewing the report and has no comment. David Howard, a spokesman for R.J. Reynolds Tobacco Co., also declined to comment, noting that his company is planning to appeal Kessler's decision. Lorillard Tobacco did not return phone calls for this story.